Method and system for manufacturing a surface using character projection lithography with variable magnification

ABSTRACT

A character projection charged particle beam writer system is disclosed comprising a variable magnification reduction lens which will allow different shot magnifications on a shot by shot basis. A method for fracturing or mask data preparation or optical proximity correction is also disclosed comprising assigning a magnification to each calculated charged particle beam writer shot. A method for forming a pattern on a surface is also disclosed comprising using a charged particle beam writer system and varying the magnification from shot to shot. A method for manufacturing an integrated circuit using optical lithography is also disclosed, comprising using a charged particle beam writer system to form a pattern on a reticle, and varying the magnification of the charged particle beam writer system from shot to shot.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/236,050, filed Aug. 21, 2009, entitled “Methodand System For Manufacturing a Surface Having Variable Sized PatternsUsing Character Projection Lithography”; which is hereby incorporated byreference for all purposes.

BACKGROUND OF THE DISCLOSURE

The present disclosure is related to lithography, and more particularlyto the design of a charged particle beam writer system and methods forusing the charged particle beam writer system to manufacture a surfacewhich may be a reticle, a wafer, or any other surface.

In the production or manufacturing of semiconductor devices, such asintegrated circuits, optical lithography may be used to fabricate thesemiconductor devices. Optical lithography is a printing process inwhich a lithographic mask or photomask manufactured from a reticle isused to transfer patterns to a substrate such as a semiconductor orsilicon wafer to create the integrated circuit. Other substrates couldinclude flat panel displays or even other reticles. Also, extremeultraviolet (EUV) or X-ray lithography are considered types of opticallithography. The reticle or multiple reticles may contain a circuitpattern corresponding to an individual layer of the integrated circuitand this pattern can be imaged onto a certain area on the substrate thathas been coated with a layer of radiation-sensitive material known asphotoresist or resist. Once the patterned layer is transferred the layermay undergo various other processes such as etching, ion-implantation(doping), metallization, oxidation, and polishing. These processes areemployed to finish an individual layer in the substrate. If severallayers are required, then the whole process or variations thereof willbe repeated for each new layer. Eventually, a combination of multiplesof devices or integrated circuits will be present on the substrate.These integrated circuits may then be separated from one another bydicing or sawing and then may be mounted into individual packages. Inthe more general case, the patterns on the substrate may be used todefine artifacts such as display pixels, holograms or magnetic recordingheads.

In the production or manufacturing of semiconductor devices, such asintegrated circuits, maskless direct write may also be used to fabricatethe semiconductor devices. Maskless direct write is a printing processin which charged particle beam lithography is used to transfer patternsto a substrate such as a semiconductor or silicon wafer to create theintegrated circuit. Other substrates could include flat panel displays,imprint masks for nano-imprinting, or even reticles. Desired patterns ofa layer are written directly on the surface, which in this case is alsothe substrate. Once the patterned layer is transferred the layer mayundergo various other processes such as etching, ion-implantation(doping), metallization, oxidation, and polishing. These processes areemployed to finish an individual layer in the substrate. If severallayers are required, then the whole process or variations thereof willbe repeated for each new layer. Some of the layers may be written usingoptical lithography while others may be written using maskless directwrite to fabricate the same substrate. Eventually, a combination ofmultiples of devices or integrated circuits will be present on thesubstrate. These integrated circuits are then separated from one anotherby dicing or sawing and then mounted into individual packages. In themore general case, the patterns on the surface may be used to defineartifacts such as display pixels, holograms or magnetic recording heads.

As indicated, in optical lithography the lithographic mask or reticlecomprises geometric patterns corresponding to the circuit components tobe integrated onto a substrate. The patterns used to manufacture thereticle may be generated utilizing computer-aided design (CAD) softwareor programs. In designing the patterns the CAD program may follow a setof predetermined design rules in order to create the reticle. Theserules are set by processing, design, and end-use limitations. An exampleof an end-use limitation is defining the geometry of a transistor in away in which it cannot sufficiently operate at the required supplyvoltage. In particular, design rules can define the space tolerancebetween circuit devices or interconnect lines. The design rules are, forexample, used to ensure that the circuit devices or lines do notinteract with one another in an undesirable manner. For example, thedesign rules are used so that lines do not get too close to each otherin a way that may cause a short circuit. The design rule limitationsreflect, among other things, the smallest dimensions that can bereliably fabricated. When referring to these small dimensions, oneusually introduces the concept of a critical dimension. These are, forinstance, defined as the smallest width of a line or the smallest spacebetween two lines, those dimensions requiring exquisite control.

One goal in integrated circuit fabrication by optical lithography is toreproduce on the substrate the original circuit design by use of thereticle. Integrated circuit fabricators are always attempting to use thesemiconductor wafer real estate as efficiently as possible. Engineerskeep shrinking the size of the circuits, either allowing an integratedcircuit with the same number of circuit elements to be smaller and useless power, or allowing an integrated circuit of the same size tocontain more circuit elements. As the size of an integrated circuitcritical dimension is reduced and its circuit density increases, thecritical dimension of the circuit pattern or physical design approachesthe resolution limit of the optical exposure tool used in opticallithography. As the critical dimensions of the circuit pattern becomesmaller and approach the resolution value of the exposure tool, theaccurate transcription of the physical design to the actual circuitpattern developed on the resist layer becomes difficult. To further theuse of optical lithography to transfer patterns having features that aresmaller than the light wavelength used in the optical lithographyprocess, a process known as optical proximity correction (OPC) has beendeveloped. OPC alters the physical design to compensate for distortionscaused by effects such as optical diffraction and the opticalinteraction of features with proximate features. OPC includes allresolution enhancement technologies performed with a reticle.

OPC may add sub-resolution lithographic features to mask patterns toreduce differences between the original physical design pattern, thatis, the design, and the final transferred circuit pattern on thesubstrate. The sub-resolution lithographic features interact with theoriginal patterns in the physical design and with each other andcompensate for proximity effects to improve the final transferredcircuit pattern. One feature that is used to improve the transfer of thepattern is a sub-resolution assist feature (SRAF). Another feature thatis added to improve pattern transference is referred to as “serifs”.Serifs are small features that can be positioned on a corner of apattern to sharpen the corner in the final transferred image. It isoften the case that the precision demanded of the surface manufacturingprocess for SRAFs is less than that for patterns that are intended toprint on the substrate, often referred to as main features. Serifs are apart of a main feature. As the limits of optical lithography are beingextended far into the sub-wavelength regime, the OPC features must bemade more and more complex in order to compensate for even more subtleinteractions and effects. As imaging systems are pushed closer to theirlimits, the ability to produce reticles with sufficiently fine OPCfeatures becomes critical. Although adding serifs or other OPC featuresto a mask pattern is advantageous, it also substantially increases thetotal feature count in the mask pattern. For example, adding a serif toeach of the corners of a square using conventional techniques adds eightmore rectangles to a mask or reticle pattern. Adding OPC features is avery laborious task, requires costly computation time, and results inmore expensive reticles. Not only are OPC patterns complex, but sinceoptical proximity effects are long range compared to minimum line andspace dimensions, the correct OPC patterns in a given location dependsignificantly on what other geometry is in the neighborhood. Thus, forinstance, a line end will have different size serifs depending on whatis near it on the reticle. This is even though the objective might be toproduce exactly the same shape on the wafer. It is conventional todiscuss the OPC-decorated patterns to be written on a reticle in termsof main features, that is features that reflect the design before OPCdecoration, and OPC features, where OPC features might include serifs,jogs, and SRAF. To quantify what is meant by slight variations, atypical slight variation in OPC decoration from neighborhood toneighborhood might be 5% to 80% of a main feature size. Note that forclarity, variations in the design of the OPC are what is beingreferenced. Manufacturing variations, such as line-edge roughness andcorner rounding, will also be present in the actual surface patterns.When these OPC variations produce substantially the same patterns on thewafer, what is meant is that the geometry on the wafer is targeted to bethe same within a specified error, which depends on the details of thefunction that that geometry is designed to perform, e.g., a transistoror a wire. Nevertheless, typical specifications are in the 2%-50% of amain feature range. There are numerous manufacturing factors that alsocause variations, but the OPC component of that overall error is oftenin the range listed. OPC shapes such as sub-resolution assist featuresare subject to various design rules, such as a rule based on the size ofthe smallest feature that can be transferred to the wafer using opticallithography. Other design rules may come from the mask manufacturingprocess or, if a character projection charged particle beam writingsystem is used to form the pattern on a reticle, from the stencilmanufacturing process. It should also be noted that the accuracyrequirement of the SRAF features on the mask may be lower than theaccuracy requirements for the main features on the mask.

Inverse lithography technology (ILT) is one type of OPC technique. ILTis a process in which a pattern to be formed on a reticle is directlycomputed from a pattern which is desired to be formed on a substratesuch as a silicon wafer. This may include simulating the opticallithography process in the reverse direction, using the desired patternon the surface as input. ILT-computed reticle patterns may be purelycurvilinear—i.e. completely non-rectilinear—and may include circular,nearly circular, annular, nearly annular, oval and/or nearly ovalpatterns. Since curvilinear patterns are difficult and expensive to formon a reticle using conventional techniques, rectilinear approximationsof the curvilinear patterns may be used. In this disclosure ILT, OPC,source mask optimization (SMO), and computational lithography are termsthat are used interchangeably.

As the minimum feature size decreases along Moore's Law, and especiallyas features with dimensions less than 50 nm on the substrate are formedusing optical lithography with a 193 nm illumination source withimmersion technology, the OPC features on a photomask become verycomplex in shape. Specifically, it will not be practical to limit theshapes on a reticle to orthogonal and rectilinear shapes and stillachieve a wafer fabrication process window sufficient to produce anacceptable process yield.

There are a number of technologies used for forming patterns on areticle, including using optical lithography or charged particle beamsystems. The most commonly used system is the variable shape beam (VSB)type, where a precise electron beam is shaped and steered onto aresist-coated surface of the reticle. These shapes are simple shapes,usually limited to rectangles of certain minimum and maximum sizes andtriangles with their three internal angles being 45 degrees, 45 degrees,and 90 degrees of certain minimum and maximum sizes. At pre-determinedlocations, doses of electrons are shot into the resist with these simpleshapes. The total writing time for this type of system increases withthe number of shots. A second type of system is a character projectionsystem, referred to as CP in this disclosure. In this case there is astencil in the system that has in it a variety of shapes which may berectilinear, arbitrary-angled linear, circular, annular, part circular,part annular, or arbitrary curvilinear shapes, and may be a connectedset of complex shapes or a group of disjointed sets of a connected setof complex shapes. An electron beam can be shot through the stencil toefficiently produce more complex patterns (i.e. CP characters, sometimesreferred to as characters) on the reticle. In theory, such a systemcould be faster than a VSB system because it can shoot more complexshapes with each time-consuming shot. Thus, an E shot with a VSB systemtakes four shots, but could be done with one shot with a characterprojection system. Note that shaped beam systems can be thought of as aspecial (simple) case of character projection, where the characters arejust simple characters, usually rectangles or 45-45-90 triangles. It isalso possible to partially expose a character. This can be done by, forinstance, blocking part of the particle beam. For example, the Edescribed above can be partially exposed as an F or an I, wheredifferent parts of the beam are cut off by an aperture. For a verycomplex reticle, one must fracture the pattern into nearly billions andsometimes approaching trillions of elemental shapes. There are, forinstance, simple rectangular shapes for a VSB system or a limited numberof characters in a character projection system. The more total instancesof elemental shapes (characters) in the pattern, the longer and moreexpensive the write time. However, for writing surfaces such as anOPC-decorated reticle where there are numerous fine variations amongeven the smaller patterns, such projection systems are todayimpractical. The number of characters that can be made available amongwhich the selection of characters by the projection machine takesminimal time is limited, today only allowing about 10-1000 characters.When faced with the plethora of slightly varying OPC patterns that arerequired to be placed on a reticle, no system or method has beenavailable which can accomplish this task.

Thus, it would be advantageous to reduce the time and expense it takesto prepare and manufacture a reticle that is used for a substrate. Moregenerally, it would be advantageous to reduce the time and expense ittakes to prepare and manufacture any surface. Toward this goal, it wouldalso be desirable to maximize the number of patterns that can be writtento the surface using CP characters, the available set of which islimited in size. Thus, there exists a need for a charged particle beamwriter system and method for manufacturing a surface that eliminates theforegoing problems associated with preparing a surface.

SUMMARY OF THE DISCLOSURE

A character projection charged particle beam writer system is disclosedcomprising a variable magnification reduction lens which will allowdifferent magnifications on a shot by shot basis.

A method for fracturing or mask data preparation or optical proximitycorrection is also disclosed comprising assigning a magnification toeach calculated charged particle beam writer shot.

A method for forming a pattern on a surface is also disclosed comprisingusing a charged particle beam writer system and varying themagnification from shot to shot.

A method for manufacturing an integrated circuit using opticallithography is also disclosed, comprising using a charged particle beamwriter system to form a pattern on a reticle, and varying themagnification of the charged particle beam writer system from shot toshot.

These and other advantages of the present disclosure will becomeapparent after considering the following detailed specification inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a character projection charged particle beam writersystem used to manufacture a surface;

FIG. 2A illustrates an annular pattern;

FIG. 2B illustrates another annular pattern having a thickness greaterthan the pattern of FIG. 2A;

FIG. 2C illustrates another annular pattern which is similar to thepattern of FIG. 2A but which is larger in overall size;

FIG. 3A illustrates an elliptical pattern;

FIG. 3B illustrates an elliptical annular pattern;

FIG. 4 illustrates a set of four rectangles arranged in a sub-resolutionassist feature (SRAF) configuration;

FIG. 5 illustrates a pattern consisting of a square with an enclosedcircular hole;

FIG. 6 illustrates a pattern consisting of the union of a circle and asquare;

FIG. 7 illustrates a complex pattern consisting of a circle surroundedby two concentric annuli;

FIG. 8 illustrates a circular pattern that can be created on a surfaceusing a parameterized glyph; and

FIG. 9 illustrates an embodiment of a conceptual flow diagram of how toprepare a surface for use in fabricating a substrate such as anintegrated circuit on a silicon wafer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The improvements and advantages of the present disclosure can beaccomplished by use of a charged particle beam writer system in whichthe de-magnification can be adjusted for each shot, and by creating andusing a shot list which contains a magnification for each shot.

Referring now to the drawings, wherein like numbers refer to like items,number 10 identifies an embodiment of a lithography system, such as aparticle beam writer system, in this case an electron beam writersystem, that employs character projection to manufacture a surface 30.The electron beam writer system 10 has an electron beam source 12 thatprojects an electron beam 14 toward an aperture plate 16. The plate 16has an aperture 18 formed therein which allows the electron beam 14 topass. Once the electron beam 14 passes through the aperture 18 it isdirected or deflected by a system of lenses (not shown) as electron beam20 toward another rectangular aperture plate or stencil mask 22. Thestencil 22 has formed therein a number of openings or apertures 24 thatdefine various types of characters 26. Each character 26 formed in thestencil 22 may be used to form a pattern 28 on a surface 30 of asubstrate 32, such as a silicon wafer, a reticle or other substrate. Inpartial exposure, partial projection, partial character projection, orvariable character projection, electron beam 20 may be positioned so asto strike or illuminate only a portion of character 26, thereby forminga pattern 28 that is a subset of character 26. An electron beam 34emerges from one of the characters 26 and passes through an electronicreduction lens 38 which reduces the size of the pattern from thecharacter 26. In commonly available charged particle beam writersystems, the reduction factor is between 10 and 60. The reduced electronbeam 40 emerges from the reduction lens 38, and is directed by a seriesof deflectors 39 onto the surface 30 as the pattern 28, which isdepicted as being in the shape of the letter “H”. The pattern 28 is areduced in size compared to the character 26 because of the reductionlens 38. The pattern 28 is drawn by using one shot of the electron beamsystem 10. This reduces the overall writing time to complete the pattern28 as compared to using a variable shape beam (VSB) projection system ormethod. Although one aperture 18 is shown being formed in the plate 16,it is possible that there may be more than one aperture in the plate 16.Although two plates 16 and 22 are shown in this example, there may beonly one plate or more than two plates each plate comprising one or moreapertures. In conventional charged particle beam writer systems thereduction lens is calibrated to provide a fixed reduction factor.

FIG. 7 illustrates an example of an ILT-generated pattern 700, such as apattern for a contact or via for an integrated circuit. A primarycircular or nearly-circular shape 702 is surrounded by two annular ornearly-annular sub-resolution assist features (SRAF), annulus 704 andannulus 706. In this disclosure, circular, circle, cylinder,cylindrical, annular, and annulus are used to describe nearly-circular,near-circle, near-cylinder, nearly-cylindrical, nearly-annular andnear-annulus respectively including their plural forms. An integratedcircuit pattern may have hundreds of thousands or millions of contact orvia patterns. However, the sizes of the circle 702, the annulus 704and/or the annulus 706 may be slightly different among the millions ofpatterns. Also, the thickness of the annulus 704 and the annulus 706 mayvary. Using VSB technology to transfer pattern 700 to a surface wouldrequire a large number of VSB shots, because of the curvilinear natureof the pattern 700. Ideally, the entire pattern 700 would be shot usingone or a few CP shots. The many variations of the pattern, however,would overflow the available capacity of a stencil. To make use of CPpractical for exposing this pattern in large numbers on a surface, oneor a few CP characters must be able to shoot a variety of sizes ofshapes 702, 704 and 706, and also a variety of thicknesses of annuli 704and 706.

FIGS. 2A-C illustrate two types of variations for an annular pattern.FIG. 2A illustrates an annular pattern 202 having an outer radius 204and a thickness 206. FIG. 2B illustrates an annular pattern 222 similarto 202. Pattern 222 has an outer radius 224 and a thickness 226. Inparticular, thickness 226 is greater than thickness 206. The outerradius 224 of pattern 222 is also greater than the outer radius 204 ofpattern 202. Specifically, the difference of outer radius 224 minusouter radius 204 is one-half the difference of thickness 226 minusthickness 206. The larger outer radius of annulus 222 compared toannulus 202 is therefore due to the increase in thickness 226 overthickness 206, and not due to a change of magnification. Priordisclosures, such as Fujimura (U.S. Pat. No. 7,759,026) have disclosed amethod for varying the width of a line by varying the shot dosage. Thistechnique may be applied to FIG. 2A & FIG. 2B patterns. Specifically,dosage variation may be used to form annulus 202 and annulus 222 on asurface using a single CP character.

FIG. 2C illustrates an annulus 212 with an outer radius 214 and athickness 216. Annulus 212 is scaled or magnified compared to annulus202. In other words, the ratio of outer radius 214 to outer radius 204is the same as the ratio of thickness 216 to thickness 206. Variablescaling is not possible in a conventional charged particle beam writersystem, because the reduction lens 38 has a fixed calibrated reductionratio or factor—typically between 10 and 60. By contrast, one embodimentof the current invention is a charged particle beam writer system inwhich the reduction lens 38 is able to reduce the pattern 26 by avariable ratio which can be specified separately for each shot.Magnification variation refers to the ability of the reduction lens 38to change or vary its magnification from shot to shot. The design of thereduction lens 38 may be electrostatic, electromagnetic, or acombination of electrostatic and electromagnetic. The reduction lens 38may consist of a single set of plates or coils, or of multiple sets ofplates and/or coils, which may be of different sizes. In one embodiment,a particular subset of plates and/or coils may be primarily or only forthe fine-level control of magnification variations. Similarly, a subsetof plates and/or coils may be primarily or only for the large-levelcontrol of magnification variation. In one embodiment the chargedparticle beam writer system may be capable of different magnificationvariations for the X-axis and Y-axis of a Cartesian plane. In anotherembodiment the magnification variation may comprise the ability to varythe magnification in multiple axes that are other than 90 degrees apart,such as 45 degrees. In another embodiment, there may be multiplemagnifications which are individually calibrated. In yet anotherembodiment, the charged particle beam writer system may interpolate whenmagnifying to a factor between points of calibration, the interpolationusing linear, quadratic or another technique. Because the precisionrequirement for the SRAFs is often less than that for main features, andbecause the curvilinear SRAFs typically would require many more VSBshots than for main feature without CP, the use of CP characters,including those from partial projection, are particularly attractive forSRAFs. Main features can also be projected using magnificationvariation. Hence annulus 212 may be an SRAF or a main feature. Usingpartial projection, a part of annulus 212 may be projected as one CPshot on the surface, each such part being subject to magnificationvariation, vastly increasing the number of shapes that can be projectedfrom a CP character containing annulus 212.

Referring again to FIG. 2A and FIG. 2C, as previously indicated, thethickness 216 of annulus 212 is larger than the thickness 206 of annulus202. By reducing the charged particle beam writer dosage when shootingannulus 212 compared to the dosage of annulus 202, thickness 216 may bereduced to be closer to or the same as thickness 206. The combination ofmagnification variation with dosage modification allows varying the sizeof a pattern or shape such as annulus 202 without changing the width ofthe pattern or shape, such as the thickness of annulus 202. One skilledin the art will recognize that other methods of CP shot modificationand/or partial projection known in the art can be combined with themagnification variation of the present disclosure to form a largevariety of patterns using one or a few CP characters.

FIG. 3A illustrates an example of an elliptical pattern 300, such as maybe output from ILT OPC processing. Pattern 300 has a major diameter 302and a minor diameter 304, such that the major diameter 302 is greaterthan the minor diameter 304. Expressed another way, pattern 300 islonger in the Y-direction of the Cartesian plane than in theX-direction. Pattern 300 can be formed on a surface by using a chargedparticle beam writer system of the current disclosure, using one shot ofa circular CP character, by specifying a Y-axis magnification greaterthan the X-axis magnification. Similarly, nearly elliptical patterns maybe formed on a surface from nearly circular CP characters.

FIG. 3B illustrates an example of an elliptical annular pattern 310. Theinterior dimension of the pattern 310 is 312 in the X-dimension and 314in the Y-dimension, where the X-dimension 312 is greater than theY-dimension 314 in this example. Pattern 310 may be formed on a surfaceusing a charged particle beam writer system of the current disclosureand an annular CP character, by specifying an X-magnification factorgreater than the Y-magnification factor. Note that because of thedifferent scaling in X and Y dimensions, the thickness of the pattern310 is not constant. Rather, the thickness 322 near the X-axis isgreater than the thickness 324 near the Y-axis. Similarly, patternswhich are nearly-elliptical annular may be formed using CP characterswhich are nearly circular. Elliptical or nearly-elliptical annularpatterns such as pattern 310 may be output from ILT OPC processing.

FIG. 4 illustrates an example of a set of four rectangles 400 which areangled at 45 degree angles with respect to the X,Y axis of the Cartesianplane. The set 400 consists of rectangle 402, rectangle 404, rectangle406 and rectangle 408. This relative formation of rectangles may beoutput as an SRAF by OPC processing, and may be output in variousslightly-different sizes. Using a charged particle beam writer system ofthe current disclosure, a single CP character containing this set offour rectangles may be used to shoot this four-rectangle SRAF in avariety of sizes by varying the magnification of the charged-particlebeam.

FIGS. 5 and 6 illustrate other types of patterns that may be output fromOPC processing in a plurality of sizes. FIG. 5 illustrates a pattern 502which consists of a circular hole within a square. FIG. 6 illustrates apattern 602 which is the union of a circle and a square. Using a chargedparticle beam writer system of the current disclosure, pattern 502 canbe written in a plurality of sizes using only a single CP character byvarying the magnification of the charged-particle beam. Similarly,pattern 602 can be written in a plurality of sizes using only a singleCP character by varying the magnification of the charged-particle beam.By using different X-axis and Y-axis magnifications, a pattern which isthe union of an ellipse and a rectangle can be written using the same CPcharacter as is used for pattern 602.

Two-dimensional maps of dosages known to be generated on a surface bysingle charged particle beam shots or combinations of charged particlebeam shots are called glyphs. Each glyph may have associated with it theposition and shot dosage information for each of the charged particlebeam shots comprising the glyph. A library of glyphs may be pre-computedand made available to fracturing or mask data preparation functions.Glyphs may also be parameterized. FIG. 8 illustrates an example of acircular pattern on a surface which represents a set of patterns thatcan be formed by a parameterized glyph. The parameter of the glyph 802is its diameter “d”, where “d” may be any value between 50 and 100units. In one embodiment, the glyph may be calculated using one or morecircular CP characters, using different shot magnifications to changethe size of the pattern formed on the surface. Magnification variationmay be combined with other known techniques of CP shot modification,including dosage variation and shot overlap, to create glyphs.

FIG. 9 is an exemplary conceptual flow diagram 250 of how to prepare areticle for use in fabricating a surface such as an integrated circuiton a silicon wafer. In a first step 252, a physical design, such as aphysical design of an integrated circuit, is designed. This can includedetermining the logic gates, transistors, metal layers, and other itemsthat are required to be found in a physical design such as that in anintegrated circuit. Next, in a step 254, optical proximity correction is(OPC) determined. In an embodiment of this disclosure this can includetaking as input a library of pre-calculated glyphs or parameterizedglyphs 276. This can also alternatively, or in addition, include takingas input a library of pre-designed CP characters 270 including complexcharacters that are to be available on a stencil 260 in a step 262. Inanother embodiment of this disclosure, an OPC step 254 may also includesimultaneous optimization of shot count or write times, and may alsoinclude a fracturing operation, a shot placement operation, a doseassignment operation, or may also include a shot sequence optimizationoperation, or other mask data preparation operations. In thisembodiment, OPC step 254 may use charged particle beam writer systeminformation 255, which may include the range of magnifications which areavailable. Once optical proximity correction is completed a mask designis developed in a step 256. Then, in a step 258, a set of shots isdetermined in a mask data preparation (MDP) operation which may includea fracturing operation, a shot placement operation, a dose assignmentoperation, or a shot sequence optimization may take place. Either of thesteps of the OPC step 254 or of the MDP step 258, or a separate programindependent of these two steps 254 or 258 can include a program fordetermining a limited number of stencil characters that need to bepresent on a stencil or a large number of glyphs or parameterized glyphsthat can be shot on the surface with a small number of shots bycombining characters that need to be present on a stencil with varyingdose, position, and degree of partial exposure to write all or a largepart of the required patterns on a reticle. It is to be understoodthroughout this disclosure that the mask data preparation step 258 doesnot include OPC. Combining OPC and any or all of the various operationsof mask data preparation in one step is contemplated in this disclosure.Mask data preparation step 258 may include a fracturing operation, andmay also comprise a pattern matching operation to match glyphs to createa mask that matches closely to the mask design. Mask data preparationmay also comprise inputting patterns to be formed on a surface with thepatterns being slightly different, selecting a set of characters to beused to form the number of patterns, the set of characters fitting on astencil mask, and the set of characters based on varying character doseor varying character position or varying the character magnification orapplying partial exposure of a character within the set of characters toreduce the shot count or total write time. A set of slightly differentpatterns on the surface may be designed to produce substantially thesame pattern on a substrate. Also, the set of characters may be selectedfrom a predetermined set of characters. Mask data preparation step 258may also include taking as input information about the charged particlebeam writer, such as the range or discrete values of magnificationsavailable. In one embodiment of this disclosure, a set of CP charactersto be made available on a stencil so that characters in the set may beselected quickly during the mask writing step 262 may be prepared for aspecific mask design in step 272 and put into a CP character library270. In that embodiment, once the mask data preparation step 258 iscompleted, a stencil is prepared in a step 260. In another embodiment ofthis disclosure, a stencil is prepared in the step 260 prior to orsimultaneous with the MDP step 258 and may be independent of theparticular mask design. In this embodiment, the characters available inthe CP character library 270 and the stencil layout are designed in step272 to output generically for many potential mask designs 256 toincorporate slightly different patterns that are likely to be output bya particular OPC program 254 or a particular MDP program 258 orparticular types of designs that characterize the physical design 252such as memories, flash memories, system on chip designs, or particularprocess technology being designed to in physical design 252, or aparticular cell library used in physical design 252, or any other commoncharacteristics that may form different sets of slightly differentpatterns in mask design 256. The stencil can include a set ofcharacters, such as a limited number of characters that was determinedin the step 258, including a set of adjustment characters. Once thestencil is completed the stencil is used in a charged particle beamwriter system, such as an electron beam system, to form a pattern on thesurface of a reticle in step 262. Each shot of the charged particle beamwriter system may have a specified magnification. After the image isformed on the reticle, the reticle undergoes various processing steps263 through which it becomes a photomask 264. The photomask may then beused in an optical lithography machine, which is shown in a step 266.Finally, in a step 268, a substrate such as a silicon wafer is produced.As has been previously described, characters in a CP library 270 may beprovided to the OPC step 254 or the MDP step 258. The CP library 270also provides characters to a character and stencil design step 272 or aglyph generation step 274. The character and stencil design step 272provides input to the stencil step 260 and to the CP character library270. The glyph generation step 274 provides information to a glyphs orparameterized glyphs library 276. Also, as has been discussed, theglyphs or parameterized glyphs library 276 provides information to theOPC step 254 or the MDP step 258.

It should be understood throughout this disclosure that the range of CPcharacter magnifications available in the reduction lens of a chargedparticle beam writer system is contemplated to be less than one.Therefore in this disclosure the words magnification andde-magnification refer to the same operation.

Throughout this disclosure the terms “calculate” and “calculation” mayinclude pre-computation, table look-up, constructive algorithms, greedyalgorithms, and iterative improvement methods, in addition to normaldeterministic methods such as an equation.

While the specification has been described in detail with respect tospecific embodiments, it will be appreciated that those skilled in theart, upon attaining an understanding of the foregoing, may readilyconceive of alterations to, variations of, and equivalents to theseembodiments. These and other modifications and variations to the presentvariable magnification charged particle beam writer system and methodsfor fracturing and for forming patterns using such a system may bepracticed by those of ordinary skill in the art, without departing fromthe spirit and scope of the present subject matter, which is moreparticularly set forth in the appended claims. Furthermore, those ofordinary skill in the art will appreciate that the foregoing descriptionis by way of example only, and is not intended to be limiting. Thus, itis intended that the present subject matter covers such modificationsand variations as come within the scope of the appended claims and theirequivalents.

1. A device for charged particle beam lithography comprising: aninputting device, wherein the inputting device reads a set of shots, andwherein each shot in the set of shots has a magnification; a characterprojection (CP) stencil containing a character pattern; and a reducinglens, wherein the reducing lens introduces magnification variation ofthe stencil character pattern when writing the pattern onto a surface,and wherein the magnification of the reducing lens can be varied fromshot to shot.
 2. The device of claim 1 wherein the magnificationvariation on one axis of the reducing lens may be different from themagnification variation on a different axis of the reducing lens.
 3. Thedevice of claim 1 wherein the reducing lens may be calibrated for aplurality of magnifications.
 4. The device of claim 3 wherein aninterpolation method is used when writing at a magnification which isbetween two calibrated magnifications.
 5. A method for fracturing ormask data preparation (MDP) or optical proximity correction (OPC)comprising: inputting patterns to be formed on a surface; determining aset of shots of character projection characters to form the patterns,wherein a magnification variation for a plurality of shots in the set ofshots is calculated; and outputting the magnification variationinformation for the plurality of shots.
 6. The method of claim 5 whereinthe magnification variation may be separately assigned for differentaxes.
 7. The method of claim 5 further comprising determining a dosagefor each shot in the set of shots.
 8. The method of claim 5 wherein themagnification variation for each shot in the set of shots is calculated.9. A method for forming a pattern on a surface comprising: using acharged particle beam writer system having a stencil mask for formingthe pattern on the surface; inputting a set of shots, wherein each shothas a magnification variation; and varying the magnification of thecharged particle beam writer system from shot to shot.
 10. The method ofclaim 9 wherein the magnification variation along one axis of thecharged particle beam writer system may be different from themagnification variation along a different axis of the charged particlebeam writer system.
 11. The method of claim 9 wherein each shot in theset of shots further comprises a shot dosage.
 12. A method formanufacturing an integrated circuit using an optical lithographicprocess, the optical lithographic process using a reticle, the methodcomprising: using a charged particle beam writer system having a stencilmask for forming a pattern on the reticle; inputting a set of shots tobe used to form the pattern on the reticle, wherein each shot has amagnification variation; and varying the magnification of the chargedparticle beam writer system from shot to shot.
 13. The method of claim12 wherein the magnification variation along one axis of the chargedparticle beam writer system may be different from the magnificationvariation along a different axis of the charged particle beam writersystem.
 14. The method of claim 12 wherein each shot in the set of shotsfurther comprises a shot dosage.
 15. A method for manufacturing anintegrated circuit, the integrated circuit having a surface, the methodcomprising: using a charged particle beam writer system having a stencilmask for forming a pattern on the surface; inputting a set of shots tobe used to form the pattern on the surface, wherein each shot has amagnification variation; and varying the magnification of the chargedparticle beam writer system from shot to shot.
 16. The method of claim15 wherein the magnification variation along one axis of the chargedparticle beam writer system may be different from the magnificationvariation along a different axis of the charged particle beam writersystem.